This invention relates to the metal silicide target material used for forming electrodes or wiring, etc. in semiconductor devices.
Recently the metal silicide films such as films of tungsten silicide or molybdenum silicide, etc. are used for the electrodes and wiring in LSI because of large integration of the LSI.
Sputtering, chemical vapor deposition processes, etc. are used for forming these silicide films and especially the sputtering process becomes a mainstream because of the productivity and reproducibility of the films and the safety of operation. The sputtering process is a method of forming the thin film of fine substance discharged by the collision of inert gas ions such as those of argon against the surface of target material constituted by metal and silicon.
Since high stress is generated in the metal silicide film if the stoichiometric compositions are used to form the metal silicide MSi.sub.2 with respect to the specific compositions of a target material, the target material containing a silicon content higher than that of the stoichiometric compositions within a scope not to increase its sheet resistance is usually used.
Furthermore, in case of the target material explained above a process to manufacture the target material of high density and less impurity has been researched for the purposes of preventing cracks from being generated during its use, uniformity of a thin film, achievement of low resistivity and avoiding the occurrence of "particles" caused by spotting electric discharge during sputtering, wherein in the field of sputtering the "particles" are used to mean coarse particulate substance adhered onto a thin film to be produced, and the occurrence of the particles on the thin film makes the thin film inferior. For example, in a case where a circuit pattern is formed by use of a thin film, the occurrence of the particles having a size exceeding the width of wiring causes the breakage of wiring, which is a serious problem concerning a semiconductor device.
For example, in JP-A-61-145828 there is disclosed a process to produce a silicide product formed by a melting process having steps of mixing both high purity and refractory metal powder and high purity silicon powder to thereby form a mixture, pressure-compacting the mixture to form a compact, heating and sintering the compact to thereby form a sintered body, and electron-beam-melting the sintered body.
Furthermore, in JP-A-61-141673 or JP-A-61-141674 there is disclosed a high density target material obtained by a process having the steps of mixing molybdenum powder or tungsten powder, compacting, forming silicide, breaking silicide pellet, and hot-pressing to thereby form a sintered body.
Moreover, as disclosed in publication No. JP-A-63-219580, in order to make a structure fine in size, there is proposed a process having the steps of performing the silicide reaction of silicon powder with the high melting point metal powder such as molybdenum, tungsten powder, etc. in vacuum to thereby make a calcined mass, and performing the hot isostatic press of the calcined mass.
Further, as described in publication No. JP-A6-41629, paying attention to the respect that the content of carbon relates to decrease in the occurrence of particles, there is disclosed a method additionally having a step of reducing both carbon and oxygen by heating in high vacuum a mixture which had been prepared by mixing metal powder and silicon powder.
In addition, as described in publication No. JP-A-8-49068, this applicant proposes a process in which the relative density of a calcined mass is made to be not less than 101% by sintering it at a high temperature of 1,200 to 1,400.degree. C. and under high pressure not less than 110 MPa.
The above explained densifying, the reducing of the impurities, and making the structure fine in size are means effective to decrease the occurrence of particles in metal silicide target materials such as molybdenum silicide or tungsten silicide, etc.
However, recently the integration in LSI is so significantly high as to decrease the width of thin films required for wiring, etc. down to the order of submicron with the result that even fine particles which were conventionally out of the question now becomes a problem awaiting solution.
According to the examination of the occurrence of particles regarding a target material obtained by use of the process proposed by this applicant and described in the above publication No. JP-A-8-49068, the significant decrease in the occurrence of particles not less than 0.3 .mu.m in size was able to be confirmed.
However, in such a severe case as to evaluate the occurrence number of particles not less than 0.2 .mu.m, it was found that the decrease was insufficient.